Every invoice you create will have a certain "status" associated with it, depending on where the invoice is in its life cycle. You can change the status of your invoice in the "Information" section of the invoice settings.
Draft: This means the invoice has been created and saved, but can't be viewed by anyone that isn't logged in to your site.
Pending: The invoice is live and ready to be viewed and paid.
Scheduled: This is used for recurring invoices that have been scheduled to be sent on a future date.
Outstanding Balance: The invoice has a past-due amount.
Paid: You got paid. Yes!
Written Off: The invoice has been voided.
Archived: The invoice is saved for your records, but clients can't access it anymore.